Magnetic resonance image distortion correction with a reference volume

Abstract

Distortion correction is provided in magnetic resonance imaging. Distortions in one volume are corrected using another volume. The isocenter of the other volume is nearer to an edge of the one volume than the isocenter of the one volume. Using data registration, the other volume is used to correct distortions in the one volume. The other volume may be acquired in little time relative to the acquisition of the one volume by having a smaller field of view, lower resolution, and/or smaller signal-to-noise ratio. The other volume may be a connecting volume for correcting distortions in two volumes to be composed together.

We claim: 
     
       1. A method for distortion correction in magnetic resonance imaging, the method comprising:
 acquiring first and second magnetic resonance volumes representing first and second different portions of a patient at a first resolution, the first and second magnetic resonance volumes having first and second field of views, and wherein the first and second different portions have an overlapping area; 
 acquiring a third magnetic resonance volume representing a third portion of the patient and having a third field of view, the third magnetic resonance volume having an isocenter in the overlapping area, having a field of view smaller than the first and the second field of view, and acquired at a second resolution less than the first resolution; 
 non-rigidly registering the third magnetic resonance volume with the first magnetic resonance volume; 
 correcting distortion in the first magnetic resonance volume based on the registering between the first and third magnetic resonance volumes; 
 non-rigidly registering the third magnetic resonance volume with the second magnetic resonance volume; 
 correcting distortion in the second magnetic resonance volume based on the registering between the second and third magnetic resonance volumes; 
 composing the distortion corrected first magnetic resonance volume with the distortion corrected second magnetic volume; and 
 generating an image as a function of the composed first and second magnetic resonance volumes. 
 
     
     
       2. The method of  claim 1  wherein acquiring the first and second magnetic resonance volumes representing the first and the second different portions of the patient comprise scanning the patient with isocenters of the first and second magnetic resonance volumes at least twenty centimeters apart, and wherein acquiring the third magnetic resonance volume comprises acquiring with an isocenter centered between the isocenters of the first and second magnetic resonance volumes and with a field of view overlapping less than 20% of each of the first and second magnetic resonance volumes. 
     
     
       3. The method of  claim 1  wherein acquiring the third magnetic resonance volume takes less than a tenth of the time required to acquire each of the first and second magnetic resonance volumes. 
     
     
       4. The method of  claim 1  wherein acquiring the first, second and third magnetic resonance volumes comprises acquiring the third magnetic resonance volumes with a lower signal to noise ratio than acquiring the first and second magnetic resonance volumes. 
     
     
       5. The method of  claim 1  wherein acquiring the first and second magnetic resonance volumes comprise acquiring, during a whole body scan, with the patient substantially stationary at different positions relative to a magnetic resonance scanner, at least one edge of the first and second magnetic resonance volumes subject to B 0  and gradient distortions. 
     
     
       6. The method of  claim 1  wherein non-rigidly registering comprises generating a transformation matrix representing differences in position of voxels. 
     
     
       7. The method of  claim 6  wherein correcting comprises applying the transformation matrix. 
     
     
       8. The method of  claim 1  wherein non-rigidly registering comprises elastically registering. 
     
     
       9. The method of  claim 1  wherein correcting comprises alpha-morphing parts of the first and second magnetic resonance volumes overlapping with the third magnetic resonance volume. 
     
     
       10. The method of  claim 1  wherein composing comprises aligning the first distortion corrected magnetic resonance volume with the second distortion corrected magnetic resonance volume and alpha blending a first region of the first distortion corrected magnetic resonance volume overlapping with the second distortion corrected magnetic resonance volume. 
     
     
       11. A system for distortion correction in magnetic resonance imaging, the system comprising:
 a magnetic resonance scanner having an isocenter, the magnetic resonance scanner configured to acquire sequential volume scans and a connective volume scan, wherein an isocenter of the connective volume scan is in an overlapping portion of the sequential volume scans, having a field of view smaller than a field of view of the sequential volume scans and a resolution less than a resolution of the sequential volume scans; 
 a patient bed operable to position different parts of a patient at the isocenter for the sequential volume scans and the connective volume scan; and 
 a processor configured to:
 receive the sequential volume scans and the connective volume scan; 
 non-rigidly register the connective volume scan with each of the sequential volume scans separately; 
 correct for magnetic field non-linearity distortion in each of the sequential volume scans separately based on the registration between the connective volume scan with each of the sequential volume scans; and 
 compose each of the distortion corrected sequential volume scans together without composing the connective volume scan. 
 
 
     
     
       12. The system of  claim 11  wherein the magnetic resonance scanner is configured to acquire the connective volume scan with fewer than ten percent of a number of voxels of each of the sequential volume scans, the connective volume scan having a lower resolution and a lower signal-to-noise ratio than each of the sequential volume scans. 
     
     
       13. The system of  claim 11  wherein the magnetic resonance scanner is configured to acquire the connective volume scan in less than ten percent of a time to acquire each of the sequential volume scans. 
     
     
       14. The system of  claim 11  wherein the magnetic resonance scanner is configured to acquire the connective volume scan overlapping ends of the sequential volumes, and wherein the processor is configured to morph the ends of the sequential volumes with a transformation matrix determined from the registration. 
     
     
       15. The system of  claim 11  wherein the processor is configured to generate an image as a function of the composed sequential volume scans. 
     
     
       16. In a non-transitory computer readable storage medium having stored therein data representing instructions executable by a programmed processor for distortion correction in magnetic resonance imaging, the storage medium comprising instructions for:
 obtaining first and second sets of voxels representing a first and a second different volumes of a patient, wherein the first and the second different volumes include an overlapping portion of the patient; 
 obtaining a third set of voxels representing a third different volume of the patient at a resolution less than the first and second sets of voxels, wherein the third different volume of the patent includes the overlapping portion of the patient, wherein an isocenter of the third set of voxels is in the overlapping portion of the patient; 
 registering the first and the second set of voxels with the third set of voxels separately, the registering generating a transformation indicating differences between the first and second sets of voxels and the third set of voxels; 
 correcting for the distortion in each of the first and second sets of voxels separately based on the transformation; and 
 generating an image as a function of the corrected first and second sets of voxels. 
 
     
     
       17. The non-transitory computer readable storage medium of  claim 16  wherein the correcting for the distortion is provided without a physics model. 
     
     
       18. The non-transitory computer readable storage medium of  claim 16  wherein registering comprises non-rigid registering.